XWiki Platform Wiki UI Main Wiki is software for managing subwikis on XWiki Platform, a generic wiki platform. Starting with version 5.3-milestone-2 and prior to versions 13.10.6 and 14.4, it's possible to inject arbitrary wiki syntax including Groovy, Python and Velocity script macros via the request (URL parameter) using the XWikiServerClassSheet if the user has view access to this sheet and another page that has been saved with programming rights, a standard condition on a public read-only XWiki installation or a private XWiki installation where the user has an account. This allows arbitrary Groovy/Python/Velocity code execution which allows bypassing all rights checks and thus both modification and disclosure of all content stored in the XWiki installation.

Also, this could be used to impact the availability of the wiki. This has been patched in versions 13.10.6 and 14.4. As a workaround, edit the affected document XWiki.XWikiServerClassSheet or WikiManager.XWikiServerClassSheet and manually perform the changes from the patch fixing the issue.

On XWiki versions 12.0 and later, it is also possible to import the document XWiki.XWikiServerClassSheet from the xwiki-platform-wiki-ui-mainwiki package version 14.4 using the import feature of the administration application as there have been no other changes to this document since XWiki 12.0.